1. Field of the Invention
The present invention relates to an aromatic polyester having an excellent heat resistance and a good melt-moldability and a process for producing the same.
2. Description of the Prior Art
Various trials to obtain a heat-resistant polyester have long been made. For example, polyethylene terephthalate obtained by polycondensation of a dicarboxylic acid with a diol (hereinafter referred to as PET) is known to be a general-purpose polyester having a melting point of 260.degree. C. and an excellent moldability. Also, like an aromatic polyester having a repeating unit of ##STR2## obtained by polycondensation of p-hydroxybenzoic acid which is one of oxy acids (for example, Ekonol.RTM. E-101 produced by Sumitomo Chemical Co., Ltd.), there are known special polyesters which are highly crystalline and have extremely high thermal stability enough not to decompose even at 300.degree. C. at all. Further, as examples of polyesters obtained by polycondensation of a dicarboxylic acid, a diol and an oxy acid, for example polyesters obtained by polycondensation of terephthalic acid, hydroquinone and p-hydroxybenzoic acid are disclosed in Japanese Patent Application Kokoku No. 47-47870. Still further, liquid-crystal polyesters are reported as a polyester which has a good melt-moldability and is suitable for uses requiring high strength and high modulus of elasticity (Japanese Patent Application Kokoku No. 56-18016 and Journal of Polymer Science : Polymer Chemistry Edition, Vol. 14, pp. 2043, 1976).
It is said that moldability and heat resistance are in an opposite relation, and polyesters combining these two properties in a good state have not yet been known. For example, the foregoing PET and liquid-crystal high polymers comprising PET and p-acetoxybenzoic acid are superior in the moldability, but cannot be used in uses requiring resistance to a temperature of 200.degree. C. or more. Aromatic polyesters like the foregoing Ekonol.RTM. E-101 are superior in the heat resistance, but its melting point exceeds 500.degree. C. so that melt-molding is very difficult. Further, the polyesters disclosed in the foregoing Japanese Patent Application Kokoku No. 47-47870, because of their molding temperature being 360.degree. C. or more, are not said to have a sufficient moldability.